2021 AMC 10A Spring Problem 13

Below is the video solution and professionally curated solution for Problem 13 of the 2021 AMC 10A Spring, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2021 AMC 10A Spring solutions, or check the answer key.

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Concepts:volume3D geometryPythagorean Theorem

Difficulty rating: 1370

13.

What is the volume of tetrahedron ABCDABCD with edge lengths AB=2,AB = 2, AC=3,AC = 3, AD=4,AD = 4, BC=13,BC = \sqrt{13}, BD=25,BD = 2\sqrt{5}, and CD=5?CD = 5?

33

232\sqrt{3}

44

333\sqrt{3}

66

Video solution:
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Written solution:

Place A=(0,0,0)A=(0,0,0), B=(2,0,0)B=(2,0,0), C=(0,3,0)C=(0,3,0), and D=(0,0,4)D=(0,0,4). Then

BC=22+32=13,BD=22+42=25,CD=32+42=5,BC=\sqrt{2^2+3^2}=\sqrt{13},\quad BD=\sqrt{2^2+4^2}=2\sqrt5,\quad CD=\sqrt{3^2+4^2}=5,

so this coordinate model matches all the given edge lengths. The tetrahedron is a rectangular-corner tetrahedron with perpendicular edge lengths 2,3,42,3,4 from AA, so its volume is

16(2)(3)(4)=4.\frac16(2)(3)(4)=4.

Thus, C is the correct answer.

Problem 13 in Other Years